I propose to continue my recent experiments on specific aspects of messenger RNA metabolism in Dictyostelium discoideum. These experiments include: 1) Molecular cloning of DNA complementary to the PS-1 mRNA. This mRNA is preferentially excluded from polysomes in early Dictyostelium development and that exclusion is associated with cataclysmic cleavage of Poly(A) tracts. The cloned PS-1 DNA will be used to quantitate the absolute amount of PS-1 and mRNA on and off polysomes and also to purify PS-1 mRNA for structural and functional studies; 2) Characterization of the actin mRNA precursor(s) synthesized in isolated nuclei. The structure of actin mRNA precursors synthesized in isolated nuclei will be defined by molecular hybridization and RNA sequencing. I propose a new sequencing procedure which exploits 5' (gamma-S)-labeled ribonucleoside triphosphates; and 3) An analysis of the structure and expression of ribosomal protein genes. We have partially purified the mRNAs from Dictyostelium ribosomal proteins and are using these mRNAs to isolate cloned genomic and cDNA fragments complementary to them. The cloned DNAs will be used to determine whether the genes for different ribosomal proteins are linked, whether they share common sequences, and whether they are coordinately expressed.